1. J. P. van der Ziel, P. S. Pershan, and L. D. Malmstrom, Phys. Rev. Lett
15 190 (1965);Phys. Rev. 143
574(1966).
2. J. Deschamps, M. Fitaire, and M. Lagoutte, Phys. Rev. Lett. 25, 1330 (1970); Rev. Appl. Phys. 7,155 (1972).
3. T. W. Barrett, H. Wohltjen, and A. Snow, Nature 301,694 (1983).
4. B. A. Zon, V. Yu. Kuperschmit, G. V. Pakhomov, and T. T. Urazbaev, JETP Lett
45 272 (1987).
5. G. H. Wagniere, Linear and Non-Linear Optical Properties of Molecules, (VCH, Basel, 1993).